Download Non-living

Living or non-living?
Characteristics of Viruses
• Non-cellular structure, no organelles
• Outer proteins coat called a capsid
• Nucleic acid (RNA or DNA)
– only contain genes for replication of new viruses
• Obligate intracellular parasites
– dont carry out any metabolic reactions on their
own
– require the cell machinery of host cells
• 50 times smaller than the average bacterial
cell
Living versus non-living
Living
• Contain genetic
material
• Contain structures
made of protein
• Have the ability to
replicate
Non-living
• Non-cellular
• Have no cellular
organelles
• Contain only one type
of nucleic acid
• Cannot reproduce by
themselves
Shapes of Viruses
Rodshaped
Round
Complex
Various viruses
Replication
• Attachment
– host cell surface proteins act as receptors
• Entry
– Virus penetrates and viral nucleic acid enters
– Capsid may be left outside
• Replication
– Viral DNA is replicated and instructs host organelles to
produce viral protein
• Assembly
– Many copies of whole virus particles are put together
• Release
– The cell bursts and the new viruses escape
Economic Importance
• Advantages
– Used to transfer genes from one organism to
another in genetic engineering
– Used to control pests
• e.g. insect virus against European pine sawfly
• Disadvantages
– Crop diseases
– Human diseases
– Animal livestock diseases
Diseases caused by viruses:
Human:
smallpox, chicken pox, shingles, warts,
verrucas (direct physical contact with
contaminated surfaces), hepatitis B.common
cold, influenza, mumps, measles (all spread by
droplet infection), polio
(droplets/faeces),German measles, rabies
(from a bite of an infected dog), Hepatitis A,
Ebola, AIDS.
• Smallpox Virus
• Chicken Pox
Mumps
• Plant: tobacco mosaic virus (gives tobacco
plant a spotted, mosaic appearance), potato
mosaic virus and sugar beet virus
• Most plant viruses are transmitted by insects
(vectors) e.g. greenfly, which suck sap.
• Animal: cowpox, foot and mouth (in cattle
and sheep), rabies (affects nervous system of
dogs mainly), distemper (dogs, fatal for
puppies unless immunised), Newcastle
disease in poultry and swine fever in pigs.
Medical Importance
• Advantages
– vaccine manufacture (e.g. Measles, mumps and
rubella - MMR)
– gene therapy (using viruses to replace abnormal
gene with normal one in diseased tissues)
• Disadvantages
– cause many infectious diseases
• Measles, mumps, rubella, influenza, common cold,
rabies
– some cancers are caused by viral infections
Human Diseases caused by viruses
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AIDS
Cold-sores
Measles, mumps and rubella (“MMR”)
Influenza and the common cold
Chicken pox and shingles
Viral meningitis
SARS
Haemorrhagic fever and Ebola
Genital warts and genital herpes
AIDS - Acquired Immune
Deficiency Syndrome
• HIV (human immunodeficiency virus) is a
retrovirus.
• HIV virus attacks helper T-lymphocytes upon
which we are dependent for our immune
system (and so can’t produce antibodies to
pathogens or to organisms that don’t normally
cause medical problems i.e. opportunistic
infections e.g. pneumonia).
Transmission - by body fluids e.g. blood, semen,
saliva. It can also be passed from mother to
child across placenta or in breast milk.
High-risk groups = Receivers of blood
transfusions, intravenous drug users (via
contaminated needles), haemophiliacs
receiving blood products and those with
multiple sexual partners of unknown status.
• Diagnosis
• Blood tests of HIV positive people will reveal
the presence of antibodies. Some HIV+ will
get rid of the virus and so are immune but for
others the virus is dormant and may turn into
full-blown AIDS at any stage.
Control and prevention:
• At present no cure and no vaccine due to rapid
mutation of virus.
Methods of prevention:
• Avoid unknown or multiple sexual partners.
• Do not share needles, toothbrushes, razors etc..
• Only use screened blood products.
• Use condoms if partner’s status unknown.
• Avoid contact (use gloves) with blood/body
fluids/wounds.
• Don’t donate blood, semen or body organs if
have AIDS or tested positive for the antibodies.
Statistics:
• Approx. 150 million people worldwide suffer
from AIDS. Number growing by 20%, every
year, especially in developing countries.
Treatment of viral disease
• Antibiotics do not work against viruses
– they are only effective against bacteria
• Vaccines
– injections of antibodies are often used as vaccine
but also as a treatment
• There has only been limited success with antiviral drugs
– Acyclovir (“Zovirax”) against Herpes simplex
i.e. treatment of coldsores.
– AZT against HIV in treatment of HIV/AIDS.